The present invention relates to an airbag apparatus that inflates an airbag to protect an occupant when an impact is applied to a vehicle.
As apparatuses for protecting an occupant from impact applied to a vehicle, airbag apparatuses having a gas generator (inflator) and an airbag are widely known. Such airbag apparatuses include side airbag apparatuses that protect an occupant from an impact applied to a vehicle from a side. In this type of apparatus, when an impact is applied from a side of a body side portion of a vehicle, a gas generator discharges inflation gas into the airbag. The discharged inflation gas causes the airbag to pop out forward from the seat back and to be inflated and deployed in a narrow space between the occupant seated in the vehicle seat and the body side portion. The inflated airbag reduces the impact that is transmitted from the side to the occupant through the body side portion.
In general, the lumbar region of the human body has a higher impact resistance than the shoulders and thorax. Thus, in a case of a side airbag apparatus for protecting a region including a shoulder and the lumbar region, it is preferable that the impact applied to the shoulder and thorax by the airbag be less than impact applied to the lumbar region.
For example, according to the side airbag apparatus disclosed in Japanese Patent No. 4103633, the interior of the airbag is divided into an upper inflation portion that corresponds to a shoulder and the thorax and a lower inflation portion that corresponds to the lumbar region. The upper and lower inflation portions are connected with each other by a communication passage. A cylindrical gas distributor, which encompasses a gas generator, is provided in the communication passage. The gas distributor includes an upper gas port for discharging inflation gas from the gas generator to the upper inflation portion and a lower gas port for discharging the inflation gas to the lower inflation portion. Since the lower gas port is larger than the upper gas port in this side airbag apparatus, a greater amount of inflation gas is supplied to the lower inflation portion by the gas distributor than to the upper inflation portion. Thus, the lower inflation portion is inflated at an earlier stage and by a higher internal pressure than the upper inflation portion. Accordingly, the lower inflation portion of the airbag is inflated to be relatively hard, and the upper inflation portion is inflated to be relatively soft. This allows an occupant to be effectively protected from an impact.
Further, the gas distributor of the side airbag apparatus disclosed in Japanese Patent No. 4103633 is formed of fabric. A lower portion of the gas distributor extends further downward than the lower end of the gas generator and forms a check valve. When the body of the occupant hits the lower portion of the inflated airbag, the internal pressure of the lower inflation portion is increased. When, as the result, the inflation gas starts flowing to the upper inflation portion through the gas distributor, the lower portion of the gas distributor overlaps onto itself and is closed. This restricts the flow of the inflation gas to the upper inflation portion.
However, in the above described side airbag apparatus, in which the lower portion of the cylindrical gas distributor is a check valve, parts that face the lower portion of the gas distributor are simply caused to overlap by the pressure of the inflation gas. In this case, the parts facing the gas distributor cannot be easily tightly closed without clearance, and it is therefore difficult to completely close the flow passage of the inflation gas. If the lower portion of the gas is open by the smallest degree, the inflation gas flows through the clearance. Also, when the internal pressure of the lower inflation portion is excessively high, the lower portion of the gas distributor receives a high pressure. As a result, the lower portion of the gas distributor may be tucked inside and inverted. In this case also, the inflation gas flows to the upper inflation portion through the gas distributor. As described so far, the check valve of the side airbag apparatus disclosed in Japanese Patent No. 4103633 does not operate in a stable manner.